It is known that even if a golf ball is putted with a ‘perfect robot’ (or any other form of precision mechanism) on a ‘perfect putting surface’, there will still be significant variation in the resulting ball-direction. The variation may be caused by spherical asymmetry in the mass and/or shape of the ball and by surface irregularities, in particular, in the dimpled-surface pattern. The dimpled pattern is an inherent part of golf-ball design and is provided to enhance aerodynamic performance.
In putting, the impact footprint (that is, the area of contact between ball and putter) has a span of the order of 5 millimeters, which is comparable with dimple-diameter. Since dimples cause voids in the contact between the impact face of the putter and the golf-ball surface, the impact footprint is rarely symmetrical. Moreover, the distribution of the striking force is not uniform across the footprint, but is a maximum at the initial point of contact, falling off rapidly towards the outer extremities of the footprint. Thus, the resultant striking force imparted by the putter on the ball is generally displaced from the ball-centre by a small, random amount. The degree and sense with which this gives rise to directional error in the resulting track of the ball from the line of strike, depends upon the extent to which the ball is struck more to one side than the other of the ideal centre-impact point; striking the ball more to the left of this point, propels it more to the right, and vice versa.
In addition to left/right (azimuthal) directional errors, the dimples similarly cause slight variations in the initial elevation trajectory. These errors can normally be ignored since they amount to slight variations in impact loft but do not measurably affect launch velocity or distance of putt. Accordingly, references to dimple-effect errors in the present context are to be understood to relate to errors in azimuth.
The errors due to the dimple effect are greater for hard-covered balls than for soft-covered balls, and less significant for long putts where the impact footprints are larger (because the striking force required is greater) so as to give a less asymmetric force distribution. Nonetheless, although dimple-effect errors are in any event small in relation to overall putting performance, they are significant because scoring in golf is heavily weighted by putt strokes.
One method of reducing dimple-effect errors is to provide golf balls with specially designed dimple patterns that distribute the impact force more evenly across the contact area. These modified dimple patterns may either cover the entire ball-surface or be limited to certain, identifiable zones; however, improving the dimple pattern for putting purposes, generally degrades the aerodynamic performance of the ball. A more practical approach instead, is to modify the impact face of the putter head itself to improve striking-force distribution so that the putter can be used advantageously with any make or pattern of golf ball.